1. Technical Field
The present disclosure is generally related to determining the absolute position of a sensor node, and more specifically to determining the absolute position of a sensor node that has been disposed in a haphazard manner.
2. Description of the Related Art
The present disclosure pertains to the field of localization of sensors. Sensors are usually deployed in a region to observe the activity in an area of interest. Different sensors are deployed to observe different activity. Acoustic sensors are deployed in a battlefield or in an urban area to monitor acoustic activity, for example, the presence of tanks in the field, to track vehicles, and identify the type of vehicles, etc. In urban settings, acoustic sensors can be deployed to detect congregation of people and the general nature of such a congregation, that is, whether the crowd is hostile or peaceful. The deployed acoustic sensors record the sound waves emanated in the vicinity and transmit to a remote hub or a central observation center where the data (sound waves) is analyzed. The type of analysis employed depends on the type of activity for which one is looking. Tracking vehicles in a field may comprise use of a tracking algorithm, while detecting people in the field may require an entirely different algorithm. In any case, the data analyzed has to be referenced to the location of the sensor. Without the knowledge of the sensor location, the data has no relevance. In a battlefield or in covert operation situations, the sensors may be deployed using an airborne vehicle such as a helicopter or airplane, or the sensors can be deployed by rockets. Whatever mechanism is used for deploying the sensors, the location of the deployed sensors may not be available. It is possible to guess at the general vicinity where the sensors land based on the location of the deploying vehicle, the speed at which the vehicle was flying, the angle at which the sensors were hurled, general wind speeds in the vicinity, the direction in which the vehicle was traveling, etc. The present disclosure presents a robust and elegant means in determining the location of the sensors.
At present, localization methods, e.g., R. L. Moses, R. M. Patterson, and W. Garber, Self localization of Acoustic sensor networks”, in Proc. of MSS meeting of the specialty group on Battlefield acoustic and seismic sensing, September 2002 include use of beacons to estimate the time of arrival (TOA) between two sensor nodes, which translates into range after multiplying the TOA with the propagation velocity of the signal in the medium. This range corresponds to the radius of a circle or a sphere, depending on whether the sensor nodes are on a plane or in three-dimensional space. If there are three such circles corresponding to three different TOAs with respect to a sensor node whose coordinates we would like to determine, then these circles would intersect at a common point giving the location of the sensor whose coordinates are desired. In this approach the location of the sensor is obtained relative to the three other sensors. In order to know the global positioning of the sensor, one must have knowledge of the global position of the three sensors. If there is a large number of sensors deployed in a field whose coordinates must be determined, one can use the above technique iteratively to determine their locations. However, that approach may result in cumulative error that grows as a function of distance from one sensor to the other.